The invention relates broadly to an apparatus and method for cementing of a well casing in a borehole. More specifically, the invention covers a cementing head for injecting a cementing plug into the well casing.
In a typical well cementing operation, a bottom cementing plug is introduced into the well casing ahead of the cement slurry. After the desired amount of cement slurry has been injected into the well casing, another plug, usually called a top plug, follows immediately behind the slurry column as it travels down the well casing. The function of the top and bottom plugs is to separate the cement slurry column from drilling muds and other fluids which can contaminate the slurry. Drilling mud or some other fluid is then pumped into the casing behind the top plug to push the cement slurry through the casing and up into the annulus between the casing and the borehole.
The cementing heads presently in use for injecting cementing plugs into a well casing are not entirely satisfactory. A primary reason is that most of the cementing heads now in use require that an operator on the rig floor inject the plug into the well casing, at the appropriate time, using a manual procedure. Because these cementing heads do not have a positive means for indicating that the plug has been injected into the casing, it can create a very hazardous situation for the operator if the plug should hang up in the head itself, or in the well casing. In addition to being unsafe, the situation described above can result in a substantial waste of material (cement slurry), and a waste of time required to shut down the cementing operation and clean up the equipment.